as far as i remember...
the LOC has two "coils" each side of the centerline, one called "yellow" at 90Hz and the other "blue" at 150Hz.
lets assume we're on ILS27, pointers centered and NOT inverted. now we're drifting off to the north. the LOC-pointer/needle moves to the left.
draw it on a piece of paper incl view to rwy and ils instrument.
then turn it up side down.
WHOA!